In U.S. Pat. No. 5,944,123 a drilling method is described involving the rotation of a drilling member, whereby drilling fluid is supplied to the drilling member to issue therefrom via an orifice provided therein. Off axis advance of the drilling member is achieved by modulating the rotational speed of the drilling member as it rotates.
Due to increasing friction with the bore hole wall at greater depths, the directional stability of this arrangement is expected to reduce when drilling a bore hole at relatively great depth, such as is generally required for drilling of a well for production of mineral hydrocarbons.